Conventionally, light source devices that radiate a laser light to ionized gas in a casing, maintain a plasma state, and generate ultraviolet rays are known. For example, in a light source described in Patent Literature 1, feeding is performed between counter electrodes disposed in a casing made of glass to generate plasma by discharge between the electrodes. The laser light is continuously radiated to the plasma, so that a laser support light to be a plasma emission is put on/maintained.